The present invention relates to a valve with a valve piston more particularly for a control or regulating valve according to the preamble of claim 1. The invention also relates to a valve equipped with this valve piston according to claim 13 and to a pressurised medium apparatus for a motor vehicle having a pressurised medium source and a hydraulic consumer according to the preamble of claim 16.
Valve pistons of valves of the kind mentioned above are used as valve bodies in the case of piston valves or also slide valves, wherein they are also occasionally referred to as valve actuators.
In general terms a valve of this kind has a valve bore in which the valve piston is axially guided and axially displaceable. A valve of this kind can thereby be formed as a control valve and has the task of controlling the start, stop as well as direction and pressure of through-flow volumes of the fluid flow in a hydraulic system. With a control valve of this kind it is thus possible to influence the flow capacity in the hydraulic system or hydraulic apparatus.
Valve pistons of this kind can however also be used in a similar way in regulating valves where the behaviour of the regulated characteristic value has an influence on the input characteristic value of the regulating valve.
Common to the said valves is the fact that the valve piston in the valve bore is subjected to a reciprocating movement which takes place in the longitudinal direction of the valve bore. When the direction of movement of the valve piston is reversed the valve piston is initially braked and then accelerated again in the opposite direction. A valve piston which is formed as a pressure balance is at some time still also biased on one side by a spring which has a hysteresis in its characteristic.
When the valve piston moves in the valve bore which is filled at least in part with a pressurised fluid, for example a pressurised oil, as the valve piston changes its direction so changes in the friction state occur, namely transitions from the sliding friction state to the sticking friction state and then again into the sliding friction state as the valve piston takes up its movement again. This makes it clear that hysteresis phenomena also occur here which together with the spring hysteresis already mentioned, lead to a corresponding displacement of the characteristic. If for example the through flow characteristic through the valve is considered then the actual through flow characteristic differs from the theoretical through flow characteristic as a result of the hysteresis phenomena mentioned.
It has already been attempted to use when controlling a valve a control signal superimposed with a vibration. A valve with a pressurised medium apparatus is also known from DE196 26 520 A1 wherein the control value is generated from at least two control value parts wherein one control value part is modulated with a first frequency and the second control value is modulated with a second frequency.
This known valve can be used for example in a hydraulic pressurized medium apparatus in order to control the operating pressure supplied to a hydraulic consumer according to a desired characteristic.
FIG. 1 of the drawing shows by way of example a characteristic curve of the operating pressure over the time which arises when using the known valve previously described. As can be readily seen from the graphs however the use of this known valve leads to vibration problems as a result of vibrations superimposed in the control. Thus if this known valve is used for controlling a hydraulic consumer in a hydraulic system the pressure vibrations apparent in both the rising and falling branch of the characteristic are transferred through the pipeline system of the hydraulic apparatus also to the hydraulic consumer so that the pressure vibrations which are present have a negative influence on the operating behaviour. Also further control members are regularly provided in the pipelines of the hydraulic system in the form of valves on which the pressure vibrations of the known valve likewise have a negative effect.
If the pressure vibrations spreading out in the pipe line system meet for example seated valves (poppet valves), then the valve cone is excited so that this excitation leads to the valve cone striking its seat. It is readily apparent that this seat impact can also cause mechanical damage to the valve seats and valve cone.
In addition to the hysteresis leading to displacements of the characteristic with the hydraulic system equipped with the known valve, problems also arise relating to pressure vibrations which lead in general to problems regarding the stability of the component parts present in the hydraulic system and also have a negative effect on the work characteristic of the hydraulic consumers present in the system, for example can result in noises occurring as a result of the pressure vibrations. AS a result of the vibration which is superimposed on the control value, with the known valve it can furthermore lead to considerable wear on the valve bore since the valve piston of the known valve is set in relatively rapid reciprocating movement in the valve bore.
The object of the present invention is therefore, in order to remove the drawbacks outlined above, to provide a valve piston and a valve equipped therewith so that on the one hand the influence of the hysteresis on the characteristic curve is reduced and on the other hand any excitation to vibration in the hydraulic system is avoided. The risk of wear on the valve bore is also to be reduced.
To achieve this the invention has the features indicated in claim 1 relating to the valve piston. Advantageous developments of the valve piston are provided in the other claims. Furthermore the invention proposes a valve according to claim 13 to solve the problem outlined above relating to the valve. A use of the valve piston is given in claim 14 and a pressurised medium apparatus with a valve according to the invention has the features of claim 16.
The invention is based on the knowledge that the undesired hysteresis phenomena in the valve characteristic are caused to a considerable extent by the friction states described above when the valve piston reverses its direction of movement. The pressure vibrations existing in the hydraulic system are produced as a result of the superimposed vibrations in the control of the known valve piston controlled with a reciprocating control value. Both problems can be solved in that a valve piston is used which can dispense with control through an oscillating control value, and which eliminates the problems when reversing the direction of movement with the changes in the friction state.
The invention therefore provides a valve piston for a control or regulating valve to be mounted displaceable and axially guided in a valve bore wherein the valve piston has a fluid throughflow region which is designed so that the valve piston can be brought into rotation by the fluid passing through the fluid throughflow region.
By the term fluid throughflow region is thereby meant an area on the valve piston which, when the valve piston is located in the valve bore of a valve and the pressurised fluid is flowing through the valve, comes into contact with the flowing pressurised fluid. In other words therefore the fluid throughflow region of the valve piston according to the invention is designed so that the valve piston is driven to rotate through the fluid throughflow region of the valve piston, namely when the pressurised fluid of the hydraulic apparatus in which the valve is located enters into the valve bore, flows past the fluid throughflow region and flows out again from the valve bore.
Thus if the pressurised fluid of the hydraulic apparatus flows through the control valve or regulating valve equipped with the valve piston according to the invention, then the valve piston is set in rotation through the fluid flow by means of the fluid throughflow region so that the processes of reversing the direction of movement with the standstills which take place inbetween which lead to the hysteresis are no longer provided. Since there is no longer the necessity to control the valve piston according to the invention with a vibrating control value, the problem of the pressure vibrations superimposed in the hydraulic system is effectively eliminated at the same time. In order to keep the valve piston according to the invention constantly in motion, thus to keep it constantly rotating about its own longitudinal axis, the valve piston according to the invention can also be constantly subject to a secondary or auxiliary flow circuit in the hydraulic system and kept permanently in motion through a vane system or the like which is mounted on the valve piston and can also be located outside of the valve bore and in active connection with the valve piston.
The valve piston according to the invention can be used in an existing valve as a replacement for its valve piston since the valve bore of the valve need not be changed but only the valve piston of the valve already present need be exchanged for the valve piston according to the invention.
The valve piston according to the invention has adjoining the fluid throughflow region an edge for opening and closing an inlet to the valve bore. The inlet to the valve bore is thereby the area which is connected for example to a delivery pump or a hydro reservoir so that pressurised fluid can be introduced through the inlet to the valve bore into the valve having the valve piston according to the invention. The fluid flowing in under pressure flows round the fluid throughflow region of the valve piston and sets it in rotation. The inlet to the valve bore can be opened and closed by means of the edge adjoining the fluid throughflow region, a control edge, whereby the valve piston is biased for example by a pre-control valve or pilot valve with pressure so that it is rotated in the valve bore, driven by the fluid throughflow region, and can be axially displaced, controlled by the pilot valve, in the valve bore for opening and closing the inlet through the control edge.
The pressurised fluid which enters the supply inlet can leave the valve bore again through an opening and is supplied through a pipeline system to a hydraulic consumer. The pressurised fluid can bear on the hydraulic consumer with a lower pressure than the delivery pressure produced by the delivery pump, for which purpose the control valve is designed with the valve piston according to the invention by way of example as a pressure reducing valve.
When the hydraulic consumer does not have to perform any work the pressurised fluid present in its upstream pipeline system, thus the pipeline system between the valve and the hydraulic consumer can be supplied through the valve piston preferably with practically no pressure to a tank for which purpose the valve piston has adjoining the fluid throughflow region an edge for opening and closing the outlet of the valve bore.
According to a further development of the invention the fluid throughflow region is thus formed so that the fluid passing through same exerts an impulse on the valve piston in the circumferential direction thereof so that the valve piston is set in rotation. To this end the fluid throughflow region can have an at least single-thread helical shaped groove profile such that the outer diameter of the groove profile, thus the flanks of the groove profile, corresponds substantially to the inner diameter of the valve bore and the core diameter of the groove, thus the diameter of the groove base is for forming a flow path between the groove flanks smaller than the inner diameter of the valve bore. When the pressurised fluid flowing into the valve bore through the inlet of same meets the valve piston it enters into a fluid throughflow region and flows over the at least single-thread helical groove profile existing there in the helical flow path between the groove flanks to an outlet of the valve bore against which for example the work or system pressure required on the consumer side has to bear, and exerts an impulse force on the valve piston as a result of the helical groove profile.
One or more spindle-shaped grooves are thus provided on the slider for the flow of pressurised fluid, thus for example oil, through the valve piston or valve slider.
When the oil flows through these grooves a change of direction of the flow takes place which is supported on the slider and transfers to this an impulse in the circumferential direction. The slider starts to rotate. As a result of the rotation of the slider still only sliding friction forces occur. Through this constant movement of the slider the characteristic hysteresis is clearly reduced. The number of grooves, the groove depth and the pitch of the groove spindle are thus influencing parameters which can influence the impulse exchange between the fluid and the slider and thus the circumferential forces as well as the rotational speed and can consequently be adapted to meet corresponding demands.
As a continuation of the invention the groove flanks run substantially at right angles to the core diameter of the groove profile so that a flow path for the pressurized fluid is produced which is substantially at right angles to the groove profile in a rectangular section. With this design the valve piston has no waist, as is the case for flow through the valve with known valve pistons.
In a continuation of the invention the fluid throughflow region of the valve piston has over substantially its entire length extension a cross-sectional surface area which can be formed circular ring-shaped in cross-section, but can also have for example a polygonal profile which is smaller than the cross-sectional surface area of the valve bore and on the cross-sectional surface area of the fluid throughflow region there is a fluid guide device which extends away outwards and which biases the valve piston with a force causing rotation as the fluid flows through.
The fluid throughflow region can therefore have instead of or in addition to the helical shaped groove profile mentioned above a fluid guide device in the form of at least one helically arranged row of pins on which the fluid flowing through the fluid throughflow region is supported and the reaction force sets the valve piston in rotation.
The fluid guide device can also be designed in the form of vane-like bodies on the cross-sectional surface area of the fluid throughflow region so that the fluid flowing through the fluid throughflow region is supported on these bodies and the reaction force sets the valve piston in rotation.
So that the valve piston does not cant or become inclined in the valve bore, the valve piston is provided in the area adjoining the fluid throughflow region with ring-shaped grooves through which a pressurised medium cushion can form in this area between the wall of the valve bore and the valve piston so as to centre the valve piston in the valve bore.
As a result of the hysteresis of a spring it is advantageous to operate the valve equipped with the valve piston according to the invention without any spring device.
It can equally be advantageous in the case of other valve designs it an additional resetting force is provided which is applied by a spring. If the valve piston according to the invention is used, biased for example through a precontrol or pilot valve with suitably high precontrol pressures, it can be advantageous if the valve piston is supported on the bottom of the valve bore through a spring. However so as not to have a negative influence on the rotation of the valve piston according to the invention it is advantageous if the spring is supported on the bottom of the valve bore substantially free of transverse forces. To this end the spring can be supported on the bottom of the valve bore through a spring pad with a moulded semi sphere in such a way that the semi-spherical shaped support point is located on the axis of rotation of the valve piston. As an alternative to this it is also possible for the spring to be supported on the bottom of the valve bore through a spring pad with sliding bearing and sliding disc whereby as a result of the presence of oil in the valve bore the friction between the sliding bearing and sliding disc is reduced so that the valve piston can turn substantially free of friction,. Finally it is also possible if the spring is supported on the bottom of the valve bore through a spring pad with an axially acting rolling bearing so that the spring is supported on the bottom of the valve bore substantially free of transverse forces. The rotation of the valve piston according to the invention about its own axis leads to the hysteresis phenomena in the characteristic of the valve equipped with the valve piston to be lifted or at least substantially reduced. Through the rotation it is thus also possible to replace the control of the valve piston otherwise required for reducing the hysteresis with a vibrating control value or however to superimpose the rotation on the vibrating control so that the resonance vibration problems already mentioned can be effectively eliminated.
As a result of the rotation of the valve slider according to the invention it is possible to reduce the wear between the slider and the valve bore since a lubricant film can be better produced through the rotation. For further improving the lubricant film it is also possible to provide indentations arranged staggered in the circumferential direction on the fluid throughflow region in the form of pockets or the like on the slider in order thus to improve the build-up of the lubricant film.
As already mentioned since the modifications required to overcome the problems described have been under taken on the valve piston according to the invention and need not be carried out on the valve bore, the valve piston according to the invention can be inserted in an already existing valve bore of a valve so that a valve with a valve piston according to the invention can be produced where the valve piston of a valve is exchanged for the valve piston according to the invention.
The valve piston according to the invention can advantageously be used as a control piston of a pressure reducing valve of a hydraulic pressurised medium apparatus. Thus the pressure reducing valve produced in this way can be used for controlling a hydraulic clutch, more particularly a hydraulic multi-plate clutch which is provided as a drive-away element of a continuously variable cone pulley belt contact gearbox. Spiral-shaped grooves provided on the valve piston in the passage area of the piston, the fluid throughflow region, direct the fluid on its way from the inlet to the work pressure outlet opening from the pressure reducing valve so that an impulse force acts on the slider and sets this in rotation. Rotation of the valve piston is thus maintained even when the valve piston changes the control edge and produces a through flow between the work pressure area and the tank connection. The production of the grooves described above can be achieved for example in that the valve piston is made from aluminium and the grooves are milled whereby the valve piston can then be provided with a hard oxide layer or the valve piston is made in cost-effective manner from plastics, for example a thermo-setting plastics through an injection moulding process and the grooves or the fluid guide devices are hereby made in the form of rows of pins or vane-like bodies together with the manufacture of the valve piston.
The valve which is equipped with the valve piston described above can be used for example in a pressure medium apparatus for a motor vehicle having a pressurised medium source and a hydraulic consumer in order to supply the hydraulic consumer with hydraulic pressurised fluid and/or to control or regulate the hydraulic consumer through the hydraulic pressurised fluid. Thus the fluid prepared by a delivery pump under pressure can flow through a pressure reducing valve equipped with the valve piston according to the invention to control a hydraulic multi-plate clutch. The spiral-shaped grooves arranged in the fluid throughflow region of the valve piston ensure that the fluid when passing through the passage area of the slider sets the valve piston in rotation so that the hysteresis phenomena described above in the characteristic of the work pressure required for controlling the multiplate clutch disappear or are at least substantially reduced by the rotation of the valve slider. Also it no longer results in pressure vibrations in the work or operating pressure to control the multi plate clutch so that the multi plate clutch, when it is used for example as a drive-away element of a continuously variable transmission, has its designated operating behaviour and the slipping engagement process of the multi plate clutch proceeds evenly and smoothly and is not disturbed by pressure vibrations in the control of the multi plate clutch.
Through the valve piston according to the invention and a valve equipped therewith, as a result of the constant rotation of the valve piston not only can the hysteresis be minimised but also the problems of pressure vibrations in the control of a hydraulic consumer can be eliminated since it is no longer absolutely necessary to bias the rotating valve piston with a vibration control value to minimise the hysteresis. The valve piston according to the invention can be used in an already existing valve bore which need not be altered for this purpose and provides as a result of the lubricant film building up through the development of rotary pressure between the valve bore and the valve piston a bearable lubricant film is which effectively eliminates the problem of wear on the valve bore.